Surgical access system and related methods

ABSTRACT

A surgical access system including a tissue distraction assembly and a tissue refraction assembly, both of which may be equipped with one or more electrodes for use in detecting the existence of (and optionally the distance and/or direction to) neural structures before, during, and after the establishment of an operative corridor to a surgical target site.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/439,889, pending, filed Feb. 22, 2017, which is a continuation ofU.S. patent application Ser. No. 14/598,043 (now U.S. Pat. No.9,610,071), filed Jan. 15, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/299,800 (now U.S. Pat. No. 8,942,801), filedJun. 9, 2014, which is a continuation of Ser. No. 14/052,271 (now U.S.Pat. No. 8,764,649), filed on Oct. 11, 2013, which is a continuation ofU.S. patent application Ser. No. 13/742,268 (now U.S. Pat. No.8,556,808), filed on Jan. 15, 2013, which is a continuation of U.S.patent application Ser. No. 12/623,016 (now U.S. Pat. No. 8,355,780),filed on Nov. 20, 2009, which is a division of U.S. patent applicationSer. No. 11/789,284 (now U.S. Pat. No. 8,016,767), filed on Apr. 23,2007, which is a continuation of U.S. patent application Ser. No.11/137,169 (now U.S. Pat. No. 7,207,949), filed on May 25, 2005, whichis a continuation of PCT Application Serial No. PCT/US04/31768, filedSep. 27, 2004, which claims the benefit of priority from U.S.Provisional Patent Application Ser. No. 60/506,136, filed Sep. 25, 2003,the entire contents of which are hereby expressly incorporated byreference into this disclosure as if set forth fully herein.

The present application also incorporates by reference the followingcommonly owned patent applications in their entireties: PCT App. Ser.No. PCT/US02/22247, entitled “System and Methods for Determining NerveProximity, Direction, and Pathology During Surgery,” filed on Jul. 11,2002; PCT App. Ser. No. PCT/US02/30617, entitled “System and Methods forPerforming Surgical Procedures and Assessments,” filed on Sep. 25, 2002;PCT App. Ser. No. PCT/US02/35047, entitled “System and Methods forPerforming Percutaneous Pedicle Integrity Assessments,” filed on Oct.30, 2002; and PCT App. Ser. No. PCT/US03/02056, entitled “System andMethods for Determining Nerve Direction to a Surgical Instrument,” filedJan. 15, 2003 (collectively “Neuro Vision PCT Applications”).

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to systems and methods forperforming surgical procedures and, more particularly, for accessing asurgical target site in order to perform surgical procedures.

2. Background of the Prior Art

A noteworthy trend in the medical community is the move away fromperforming surgery via traditional “open” techniques in favor ofminimally invasive or minimal access techniques. Open surgicaltechniques are generally undesirable in that they typically requirelarge incisions and high amounts of tissue displacement to gain accessto the surgical target site, which produces concomitantly high amountsof pain, lengthened hospitalization (increasing health care costs), andhigh morbidity in the patient population. Less-invasive surgicaltechniques (including so-called “minimal access” and “minimallyinvasive” techniques) are gaining favor due to the fact that theyinvolve accessing the surgical target site via incisions ofsubstantially smaller size with greatly reduced tissue displacementrequirements. This, in turn, reduces the pain, morbidity and costassociated with such procedures. The access systems developed to date,however, fail in various respects to meet all the needs of the surgeonpopulation.

One drawback associated with prior art surgical access systems relatesto the ease with which the operative corridor can be created, as well asmaintained over time, depending upon the particular surgical targetsite. For example, when accessing surgical target sites located beneathor behind musculature or other relatively strong tissue (such as, by wayof example only, the psoas muscle adjacent to the spine), it has beenfound that advancing an operative corridor-establishing instrumentdirectly through such tissues can be challenging and/or lead to unwantedor undesirable effects (such as stressing or tearing the tissues). Whilecertain efforts have been undertaken to reduce the trauma to tissuewhile creating an operative corridor, such as (by way of example only)the sequential dilation system of U.S. Pat. No. 5,792,044 to Foley etal., these attempts are nonetheless limited in their applicability basedon the relatively narrow operative corridor. More specifically, based onthe generally cylindrical nature of the so-called “working cannula,” thedegree to which instruments can be manipulated and/or angled within thecannula can be generally limited or restrictive, particularly if thesurgical target site is a relatively deep within the patient.

Efforts have been undertaken to overcome this drawback, such as shown inU.S. Pat. No. 6,524,320 to DiPoto, wherein an expandable portion isprovided at the distal end of a cannula for creating a region ofincreased cross-sectional area adjacent to the surgical target site.While this system may provide for improved instrument manipulationrelative to sequential dilation access systems (at least at deep siteswithin the patient), it is nonetheless flawed in that the deployment ofthe expandable portion may inadvertently compress or impinge uponsensitive tissues adjacent to the surgical target site. For example, inanatomical regions having neural and/or vasculature structures, such ablind expansion may cause the expandable portion to impinge upon thesesensitive tissues and cause neural and/or vasculature compromise, damageand/or pain for the patient.

This highlights yet another drawback with the prior art surgical accesssystems, namely, the challenges in establishing an operative corridorthrough or near tissue having major neural structures which, ifcontacted or impinged, may result in neural impairment for the patient.Due to the threat of contacting such neural structures, efforts thus farhave largely restricted to establishing operative corridors throughtissue having little or substantially reduced neural structures, whicheffectively limits the number of ways a given surgical target site canbe accessed. This can be seen, by way of example only, in the spinalarts, where the exiting nerve roots and neural plexus structures in thepsoas muscle have rendered a lateral or far lateral access path(so-called trans-psoas approach) to the lumbar spine virtuallyimpossible. Instead, spine surgeons are largely restricted to accessingthe spine from the posterior (to perform, among other procedures,posterior lumbar interbody fusion (PLIF)) or from the anterior (toperform, among other procedures, anterior lumbar interbody fusion(ALT)).

Posterior-access procedures involve traversing a shorter distance withinthe patient to establish the operative corridor, albeit at the price ofoftentimes having to reduce or cut away part of the posterior bonystructures (i.e. lamina, facets, spinous process) in order to reach thetarget site (which typically comprises the disc space). Anterior-accessprocedures are relatively simple for surgeons in that they do notinvolve reducing or cutting away bony structures to reach the surgicaltarget site. However, they are nonetheless disadvantageous in that theyrequire traversing through a much greater distance within the patient toestablish the operative corridor, oftentimes requiring an additionalsurgeon to assist with moving the various internal organs out of the wayto create the operative corridor.

The present invention is directed at eliminating, or at least minimizingthe effects of, the above-identified drawbacks in the prior art.

SUMMARY OF THE INVENTION

The present invention accomplishes this goal by providing a novel accesssystem and related methods which involve detecting the existence of (andoptionally the distance and/or direction to) neural structures before,during, and after the establishment of an operative corridor through (ornear) any of a variety of tissues having such neural structures which,if contacted or impinged, may otherwise result in neural impairment forthe patient. It is expressly noted that, although described hereinlargely in terms of use in spinal surgery, the access system of thepresent invention is suitable for use in any number of additionalsurgical procedures wherein tissue having significant neural structuresmust be passed through (or near) in order to establish an operativecorridor.

According to one broad aspect of the present invention, the accesssystem comprises a tissue distraction assembly and a tissue retractionassembly, both of which may be equipped with one or more electrodes foruse in detecting the existence of (and optionally the distance and/ordirection to) neural structures. The tissue distraction assembly (inconjunction with one or more elements of the tissue retraction assembly)is capable of, as an initial step, distracting a region of tissuebetween the skin of the patient and the surgical target site. The tissueretraction assembly is capable of, as a secondary step, being introducedinto this distracted region to thereby define and establish theoperative corridor. Once established, any of a variety of surgicalinstruments, devices, or implants may be passed through and/ormanipulated within the operative corridor depending upon the givensurgical procedure. The electrode(s) are capable of, during both tissuedistraction and retraction, detecting the existence of (and optionallythe distance and/or direction to) neural structures such that theoperative corridor may be established through (or near) any of a varietyof tissues having such neural structures which, if contacted orimpinged, may otherwise result in neural impairment for the patient. Inthis fashion, the access system of the present invention may be used totraverse tissue that would ordinarily be deemed unsafe or undesirable,thereby broadening the number of manners in which a given surgicaltarget site may be accessed.

The tissue distraction assembly may include any number of componentscapable of performing the necessary distraction. By way of example only,the tissue distraction assembly may include a K-wire, an initial dilatorof split construction, and one or more dilators of traditional (that is,non-split) construction for performing the necessary tissue distractionto receive the remainder of the tissue retractor assembly thereafter.One or more electrodes may be provided on one or more of the K-wire anddilator(s) to detect the presence of (and optionally the distance and/ordirection to) neural structures during tissue distraction.

The tissue retraction assembly may include any number of componentscapable of performing the necessary retraction. By way of example only,the tissue retraction assembly may include one or more retractor bladesextending from a handle assembly. The handle assembly may be manipulatedto open the retractor assembly; that is, allowing the retractor bladesto separate from one another (simultaneously or sequentially) to createan operative corridor to the surgical target site. In a preferredembodiment, this is accomplished by maintaining a posterior retractorblade in a fixed position relative to the surgical target site (so as toavoid having it impinge upon any exiting nerve roots near the posteriorelements of the spine) while the additional retractor blades (i.e.cephalad-most and caudal-most blades) are moved or otherwise translatedaway from the posterior retractor blade (and each other) so as to createthe operative corridor in a fashion that doesn't infringe upon theregion of the exiting nerve roots.

The retractor blades may be optionally dimensioned to receive and directa rigid shim element to augment the structural stability of theretractor blades and thereby ensure the operative corridor, onceestablished, will not decrease or become more restricted, such as mayresult if distal ends of the retractor blades were permitted to “slide”or otherwise move in response to the force exerted by the displacedtissue. In a preferred embodiment, only the posterior retractor blade isequipped with such a rigid shim element. In an optional aspect, thisshim element may be advanced into the disc space after the posteriorretractor blade is positioned, but before the retractor is opened intothe fully retracted position. The rigid shim element is preferablyoriented within the disc space such that is distracts the adjacentvertebral bodies, which serves to restore disc height. It alsopreferably advances a sufficient distance within the disc space(preferably past the midline), which serves the dual purpose ofpreventing post-operative scoliosis and forming a protective barrier(preventing the migration of tissue (such as nerve roots) into theoperative field and the inadvertent advancement of instruments outsidethe operative field).

The retractor blades may optionally be equipped with a mechanism fortransporting or emitting light at or near the surgical target site toaid the surgeon's ability to visualize the surgical target site,instruments and/or implants during the given surgical procedure.According to one embodiment, this mechanism may comprise, but need notbe limited to, coupling one or more light sources to the retractorblades such that the terminal ends are capable of emitting light at ornear the surgical target site. According to another embodiment, thismechanism may comprise, but need not be limited to, constructing theretractor blades of suitable material (such as clear polycarbonate) andconfiguration such that light may be transmitted generally distallythrough the walls of the retractor blade light to shine light at or nearthe surgical target site. This may be performed by providing theretractor blades having light-transmission characteristics (such as withclear polycarbonate construction) and transmitting the light almostentirely within the walls of the retractor blade (such as by frosting orotherwise rendering opaque portions of the exterior and/or interior)until it exits a portion along the interior (or medially-facing) surfaceof the retractor blade to shine at or near the surgical target site. Theexit portion may be optimally configured such that the light is directedtowards the approximate center of the surgical target site and may beprovided along the entire inner periphery of the retractor blade or oneor more portions therealong.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a perspective view of a tissue retraction assembly (in use)forming part of a surgical access system according to the presentinvention;

FIGS. 2-3 are perspective views illustrating the front and back of ashim element for use with a posterior retractor blade of the retractoraccording to the retractor of the present invention;

FIGS. 4-5 are perspective views illustrating the front and back of anarrow retractor extender for use with one of a cephalad and caudalretractor blade according to the retractor of the present invention;

FIGS. 6-7 are perspective views illustrating the front and back of awide retractor extender for use with one of a cephalad and caudalretractor blade according to the retractor of the present invention;

FIG. 8 is a perspective, partially exploded view of the refractorassembly of the present invention, without the retractor blades;

FIG. 9 is a perspective view illustrating the components and use of aninitial distraction assembly (i.e. K-wire, an initial dilating cannulawith handle, and a split-dilator housed within the initial dilatingcannula) forming part of the surgical access system according to thepresent invention, for use in distracting to a surgical target site(i.e. annulus);

FIG. 10 is a perspective view illustrating the K-wire and split-dilatorof the initial distraction assembly with the initial dilating cannulaand handle removed;

FIG. 11 is a posterior view of the vertebral target site illustratingthe split-dilator of the present invention in use distracting in agenerally cephalad-caudal fashion according to one aspect of the presentinvention;

FIG. 12 is a side view illustrating the use of a secondary distractionassembly (comprising a plurality of dilating cannulae over the K-wire)to further distract tissue between the skin of the patient and thesurgical target site according to the present invention;

FIG. 13 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending there from (posterior, cephalad-most, and caudal-most)disposed over the secondary distraction assembly of FIG. 12 (shown in afirst, closed position);

FIG. 14 is a side view of a retractor assembly according to the presentinvention, comprising a handle assembly having three (3) retractorblades extending there from (posterior, cephalad-most, and caudal-most)with the secondary distraction assembly of FIG. 12 removed and shimelement introduced;

FIGS. 15-16 are perspective and top views, respectively, of theretractor assembly in a second, opened (i.e. retracted) position tothereby create an operative corridor to a surgical target site accordingto the present invention;

FIGS. 17-18 are perspective and side views, respectively, of theretractor assembly in the second, opened (i.e. retracted) position (withthe secondary distraction assembly removed) and with the retractorextenders of FIGS. 4-5 and 6-7 coupled to the retractor according to thepresent invention.

FIG. 19 is a perspective view of an exemplary nerve monitoring systemcapable of performing nerve monitoring before, during and after thecreating of an operative corridor to a surgical target site using thesurgical access system in accordance with the present invention;

FIG. 20 is a block diagram of the nerve monitoring system shown in FIG.19; and

FIGS. 21-22 are screen displays illustrating exemplary features andinformation communicated to a user during the use of the nervemonitoring system of FIG. 19.

DESCRIPTION THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. It is furthermore to be readily understood that,although discussed below primarily within the context of spinal surgery,the surgical access system of the present invention may be employed inany number of anatomical settings to provide access to any number ofdifferent surgical target sites throughout the body. The surgical accesssystem disclosed herein boasts a variety of inventive features andcomponents that warrant patent protection, both individually and incombination.

The present invention involves accessing a surgical target site in afashion less invasive than traditional “open” surgeries and doing so ina manner that provides access in spite of the neural structures requiredto be passed through (or near) in order to establish an operativecorridor to the surgical target site. Generally speaking, the surgicalaccess system of the present invention accomplishes this by providing atissue distraction assembly and a tissue retraction assembly, both ofwhich may be equipped with one or more electrodes for use in detectingthe existence of (and optionally the distance and/or direction to)neural structures.

These electrodes are preferably provided for use with a nervesurveillance system such as, by way of example, the type shown anddescribed in the co-pending and commonly assigned NeuroVision PCTApplications referenced above, the entire contents of which areexpressly incorporated by reference as if set forth herein in theirentirety. Generally speaking, this nerve surveillance system is capableof detecting the existence of (and optionally the distance and/ordirection to) neural structures during the distraction and retraction oftissue by detecting the presence of nerves by applying a stimulationsignal to such instruments and monitoring the evoked EMG signals fromthe myotomes associated with the nerves being passed by the distractionand retraction systems of the present invention. In so doing, the systemas a whole (including the surgical access system of the presentinvention) may be used to form an operative corridor through (or near)any of a variety of tissues having such neural structures, particularlythose which, if contacted or impinged, may otherwise result in neuralimpairment for the patient. In this fashion, the access system of thepresent invention may be used to traverse tissue that would ordinarilybe deemed unsafe or undesirable, thereby broadening the number ofmanners in which a given surgical target site may be accessed.

The tissue distraction assembly of the present invention (comprising aK-wire, an initial dilator, and a split-dilator disposed within theinitial dilator) is employed to distract the tissues extending betweenthe skin of the patient and a given surgical target site (preferablyalong the posterior region of the target intervertebral disc). Asecondary distraction assembly (i.e. a plurality of sequentiallydilating cannulae) may optionally be employed after the initialdistraction assembly to further distract the tissue. Once distracted,the resulting void or distracted region within the patient is ofsufficient size to accommodate a tissue retraction assembly of thepresent invention. More specifically, the tissue retraction assembly(comprising a plurality of retractor blades extending from a handleassembly) may be advanced relative to the secondary distraction assemblysuch that the retractor blades, in a first, closed position, areadvanced over the exterior of the secondary distraction assembly. Atthat point, the handle assembly may be operated to move the retractorblades into a second, open or “retracted” position to create anoperative corridor to the surgical target site.

According to one aspect of the invention, following (or before) thisretraction, a posterior shim element (which is preferably slideablyengaged with the posterior retractor blade) may be advanced such that adistal shim extension in positioned within the posterior region of thedisc space. If done before retraction, this helps ensure that theposterior retractor blade will not move posteriorly during theretraction process, even though the other retractor blades (i.e.cephalad-most and caudal-most) are able to move and thereby create anoperative corridor. Fixing the posterior retractor blade in this fashionserves several important functions. First, the distal end of the shimelement serves to distract the adjacent vertebral bodies, therebyrestoring disc height. It also rigidly couples the posterior retractorblade in fixed relation relative to the vertebral bodies. The posteriorshim element also helps ensure that surgical instruments employed withinthe operative corridor are incapable of being advanced outside theoperative corridor, preventing inadvertent contact with the exitingnerve roots during the surgery. Once in the appropriate retracted state,the cephalad-most and caudal-most retractor blades may be locked inposition and, thereafter, retractor extenders advanced therealong toprevent the ingress or egress of instruments or biological structures(i.e. nerves, vasculature, etc. . . .) into or out of the operativecorridor. Once the operative corridor is established, any of a varietyof surgical instruments, devices, or implants may be passed throughand/or manipulated within the operative corridor depending upon thegiven surgical procedure.

FIG. 1 illustrates a tissue retraction assembly 10 forming part of asurgical access system according to the present invention. Theretraction assembly 10 includes a plurality of retractor bladesextending from a handle assembly 20. By way of example only, the handleassembly 20 is provided with a first retractor blade 12, a secondretractor blade 16, and a third retractor blade 18. The retractorassembly 10 is shown in a fully retracted or “open” configuration, withthe retractor blades 12, 16, 18 positioned a distance from one anotherso as to form an operative corridor 15 there between and extending to asurgical target site (e.g. an annulus of an intervertebral disc).Although shown and described below with regard to the three-bladedconfiguration, it is to be readily appreciated that the number ofretractor blades may be increased or decreased without departing fromthe scope of the present invention. Moreover, although described andshown herein with reference to a generally lateral approach to a spinalsurgical target site (with the first blade 12 being the “posterior”blade, the second blade 16 being the “cephalad-most” blade, and thethird blade 18 being the “caudal-most” blade), it will be appreciatedthat the retractor assembly 10 of the present invention may find use inany number of different surgical approaches, including generallyposterior, generally postero-lateral, generally anterior and generallyantero-lateral.

The retractor blades 12, 16, 18 may be equipped with various additionalfeatures or components. By way of example only, posterior retractorblade 12 may be equipped with a shim element 22 (shown more clearly inFIGS. 2-3). Shim element 22 serves to distract the adjacent vertebralbodies (thereby restoring disc height), helps secure the retractorassembly 10 relative to the surgical target site, and forms a protectivebarrier to prevent the ingress or egress of instruments or biologicalstructures (i.e. nerves, vasculature, etc. . . . ) into or out of theoperative corridor. Each of the remaining retractor blades(cephalad-most blade 16 and caudal-most blade 18) may be equipped with arefractor extender, such as the narrow refractor extender 24 shown inFIGS. 4-5 or the wide retractor extender 25 shown in FIGS. 6-7. Theretractor extenders 24/25 extend from the cephalad-most and caudal-mostretractor blades 16, 18 to form a protective barrier to prevent theingress or egress of instruments or biological structures (i.e. nerves,vasculature, etc. . . . ) into or out of the operative corridor 15.

According to the present invention, any or all of the retractor blades12, 16, 18, the shim element 22 and/or the retractor extenders 24/25 maybe provided with one or more electrodes 39 (preferably at their distalregions) equipped for use with a nerve surveillance system, such as, byway of example, the type shown and described in the NeuroVision PCTApplications. Each of the shim element 22 and/or the retractor extenders24/25 may also be equipped with a mechanism to selectively andreleasably engage with the respective retractor blades 12, 16, 18. Byway of example only, this may be accomplished by configuring the shimelement 22 and/or the retractor extenders 24/25 with a tab element 27capable of engaging with corresponding rachet-like grooves (shown at 29in FIG. 1) along the inner-facing surfaces of the retractor blades 12,16, 18. Each of the shim element 22 and/or the retractor extenders 24/25is provided with a pair of engagement elements 37 having, by way ofexample only, a generally dove-tailed cross-sectional shape. Theengagement elements 37 are dimensioned to engage with receiving portionson the respective retractor blades 12, 16, 18. In a preferredembodiment, each of the shim element 22 and/or the retractor extenders24/25 are provided with an elongate slot 43 for engagement with aninsertion tool (not shown). Each tab member 27 is also equipped with anenlarged tooth element 49 which engages within corresponding grooves 29provided along the inner surface of the retractor blades 12, 16, 18.

The handle assembly 20 may be coupled to any number of mechanisms forrigidly registering the handle assembly 20 in fixed relation to theoperative site, such as through the use of an articulating arm mountedto the operating table. The handle assembly 20 includes first and secondarm members 26, 28 hingedly coupled via coupling mechanism showngenerally at 30. The cephalad-most retractor blade 16 is rigidly coupled(generally perpendicularly) to the end of the first arm member 26. Thecaudal-most retractor blade 18 is rigidly coupled (generallyperpendicularly) to the end of the second arm member 28. The posteriorretractor blade 12 is rigidly coupled (generally perpendicularly to) atranslating member 17, which is coupled to the handle assembly 20 via alinkage assembly shown generally at 14. The linkage assembly 14 includesa roller member 34 having a pair of manual knob members 36 which, whenrotated via manual actuation by a user, causes teeth 35 on the rollermember 34 to engage within ratchet-like grooves 37 in the translatingmember 17. Thus, manual operation of the knobs 36 causes the translatingmember 17 to move relative to the first and second arm members 26, 28.

Through the use of handle extenders 31, 33 (FIG. 8), the arms 26, 28 maybe simultaneously opened such that the cephalad-most and caudal-mostretractor blades 16, 18 move away from one another. In this fashion, thedimension and/or shape of the operative corridor 15 may be tailoreddepending upon the degree to which the translating member 17 ismanipulated relative to the arms 26, 28. That is, the operative corridor15 may be tailored to provide any number of suitable cross-sectionalshapes, including but not limited to a generally circular cross-section,a generally ellipsoidal cross-section, and/or an oval cross-section.Optional light emitting devices 39 may be coupled to one or more of theretractor blades 12, 16, 18 to direct light down the operative corridor15.

FIG. 9 illustrates an initial distraction assembly 40 forming part ofthe surgical access system according to the present invention. Theinitial distraction assembly 40 includes a K-wire 42, an initialdilating cannula 44 with handle 46, and a split-dilator 48 housed withinthe initial dilating cannula 44. In use, the K-wire 42 and split-dilator48 are disposed within the initial dilating cannula 44 and the entireassembly 40 advanced through the tissue towards the surgical target site(i.e. annulus). Again, this is preferably accomplished while employingthe nerve detection and/or direction features described above. After theinitial dilating assembly 40 is advanced such that the distal ends ofthe split-dilator 48 and initial dilator 44 are positioned within thedisc space (FIG. 9), the initial dilator 44 and handle 46 are removed(FIG. 10) to thereby leave the split-dilator 48 and K-wire 42 in place.As shown in FIG. 11, the split-dilator 48 is thereafter split such thatthe respective halves 48 a, 48 b are separated from one another todistract tissue in a generally cephalad-caudal fashion relative to thetarget site. The split dilator 48 may thereafter be relaxed (allowingthe dilator halves 48 a, 48 b to come together) and rotated such thatthe dilator halves 48 a, 48 b are disposed in the anterior-posteriorplane. Once rotated in this manner, the dilator halves 48 a, 48 b areagain separated to distract tissue in a generally anterior-posteriorfashion. Each dilator halve 48 a, 48 b may be, according to the presentinvention, provided with one or more electrodes (preferably at theirdistal regions) equipped for use with a nerve surveillance system, suchas, by way of example, the type shown and described in the NeuroVisionPCT Applications.

Following this initial distraction, a secondary distraction may beoptionally undertaken, such as via a sequential dilation system 50 asshown in FIG. 12. According to the present invention, the sequentialdilation system 50 may include the K-wire 42, the initial dilator 44,and one or more supplemental dilators 52, 54 for the purpose of furtherdilating the tissue down to the surgical target site. Once again, eachcomponent of the secondary distraction assembly 50 (namely, the K-wire42, the initial dilator 44, and the supplemental dilators 52, 54 may be,according to the present invention, provided with one or more electrodes(preferably at their distal regions) equipped for use with a nervesurveillance system, such as, by way of example, the type shown anddescribed in the NeuroVision PCT Applications.

As shown in FIG. 13, the retraction assembly 10 of the present inventionis thereafter advanced along the exterior of the sequential dilationsystem 50. This is accomplished by maintaining the retractor blades 12,16, 18 in a first, closed position (with the retractor blades 12-16 ingenerally abutting relation to one another). Once advanced to thesurgical target site, the sequential dilation assembly 50 may be removedand the shim element 22 engaged with the posterior refractor blade 12such that the distal end thereof extends into the disc space as shown inFIG. 14. At this point, the handle assembly 20 may be operated to movethe retractor blades 16, 18 into a second, open or “retracted” positionas shown generally in FIGS. 15-16. As one can see, the posteriorretractor blade 12 is allowed to stay in the same general positionduring this process, such that the cephalad-most and caudal-mostrefractor blades 14, 16 move away from the posterior retractor blade 12.At this point, the narrow and wide retractor extenders 24, 25 may beengaged with the caudal-most retractor blade 18 and cephalad-mostretractor blade 16, respectively, as shown in FIGS. 17-18.

As mentioned above, any number of distraction components and/orretraction components (including but not limited to those describedherein) may be equipped to detect the presence of (and optionally thedistance and/or direction to) neural structures during the steps tissuedistraction and/or retraction. This is accomplished by employing thefollowing steps: (1) one or more stimulation electrodes are provided onthe various distraction and/or retraction components; (2) a stimulationsource (e.g. voltage or current) is coupled to the stimulationelectrodes; (3) a stimulation signal is emitted from the stimulationelectrodes as the various components are advanced towards or maintainedat or near the surgical target site; and (4) the patient is monitored todetermine if the stimulation signal causes muscles associated withnerves or neural structures within the tissue to innervate. If thenerves innervate, this may indicate that neural structures may be inclose proximity to the distraction and/or retraction components.

Neural monitoring may be accomplished via any number of suitablefashions, including but not limited to observing visual twitches inmuscle groups associated with the neural structures likely to found inthe tissue, as well as any number of monitoring systems, including butnot limited to any commercially available “traditional” electromyography(EMG) system (that is, typically operated by a neurophysiologist). Suchmonitoring may also be carried out via the surgeon-driven EMG monitoringsystem shown and described in the following commonly owned andco-pending NeuroVision PCT Applications referenced above. In any case(visual monitoring, traditional EMG and/or surgeon-driven EMGmonitoring), the access system of the present invention mayadvantageously be used to traverse tissue that would ordinarily bedeemed unsafe or undesirable, thereby broadening the number of mannersin which a given surgical target site may be accessed.

FIGS. 19-20 illustrate, by way of example only, a monitoring system 120of the type disclosed in the NeuroVision PCT Applications suitable foruse with the surgical access system 10 of the present invention. Themonitoring system 120 includes a control unit 122, a patient module 124,and an EMG harness 126 and return electrode 128 coupled to the patientmodule 124, and a cable 132 for establishing electrical communicationbetween the patient module 124 and the surgical access system of thepresent invention (retractor assembly 10 of FIG. 1 and distractionassemblies 40, 50 of FIGS. 9-12). More specifically, this electricalcommunication can be achieved by providing, by way of example only, ahand-held stimulation controller 152 capable of selectively providing astimulation signal (due to the operation of manually operated buttons onthe hand-held stimulation controller 152) to one or more connectors 156a, 156 b, 156 c. The connectors 156 a, 156 b, 156 c are suitable toestablish electrical communication between the hand-held stimulationcontroller 152 and (by way of example only) the stimulation electrodeson the K-wire 42, the dilators 44, 48, 52, 54, the refractor blades 12,16, 18 and/or the shim members 22, 24, 25 (collectively “surgical accessinstruments”).

In order to use the monitoring system 120, then, these surgical accessinstruments must be connected to the connectors 156 a, 156 b and/or 156c, at which point the user may selectively initiate a stimulation signal(preferably, a current signal) from the control unit 122 to a particularsurgical access instruments. Stimulating the electrode(s) on thesesurgical access instruments before, during and/or after establishingoperative corridor will cause nerves that come into close or relativeproximity to the surgical access instruments to depolarize, producing aresponse in a myotome associated with the innervated nerve.

The control unit 122 includes a touch screen display 140 and a base 142,which collectively contain the essential processing capabilities(software and/or hardware) for controlling the monitoring system 120.The control unit 122 may include an audio unit 118 that emits soundsaccording to a location of a surgical element with respect to a nerve.The patient module 124 is connected to the control unit 122 via a datacable 144, which establishes the electrical connections andcommunications (digital and/or analog) between the control unit 122 andpatient module 124. The main functions of the control unit 122 includereceiving user commands via the touch screen display 140, activatingstimulation electrodes on the surgical access instruments, processingsignal data according to defined algorithms, displaying receivedparameters and processed data, and monitoring system status and reportfault conditions. The touch screen display 140 is preferably equippedwith a graphical user interface (GUI) capable of communicatinginformation to the user and receiving instructions from the user. Thedisplay 140 and/or base 142 may contain patient module interfacecircuitry (hardware and/or software) that commands the stimulationsources, receives digitized signals and other information from thepatient module 124, processes the EMG responses to extractcharacteristic information for each muscle group, and displays theprocessed data to the operator via the display 140.

In one embodiment, the monitoring system 120 is capable of determiningnerve direction relative to one or more of the K-wire 42, the dilators44, 48, 52, 54, the retractor blades 12, 16, 18 and/or the shim elements22, 24, 25 before, during and/or following the creation of an operativecorridor to a surgical target site. Monitoring system 120 accomplishesthis by having the control unit 122 and patient module 124 cooperate tosend electrical stimulation signals to one or more of the stimulationelectrodes provided on these instruments. Depending upon the location ofthe surgical access system 10 within a patient (and more particularly,to any neural structures), the stimulation signals may cause nervesadjacent to or in the general proximity of the surgical access system 10to depolarize. This causes muscle groups to innervate and generate EMGresponses, which can be sensed via the EMG harness 126. The nervedirection feature of the system 120 is based on assessing the evokedresponse of the various muscle myotomes monitored by the system 120 viathe EMG harness 126.

By monitoring the myotomes associated with the nerves (via the EMGharness 126 and recording electrode 127) and assessing the resulting EMGresponses (via the control unit 122), the surgical access system 10 iscapable of detecting the presence of (and optionally the distant and/ordirection to) such nerves. This provides the ability to activelynegotiate around or past such nerves to safely and reproducibly form theoperative corridor to a particular surgical target site, as well asmonitor to ensure that no neural structures migrate into contact withthe surgical access system 10 after the operative corridor has beenestablished. In spinal surgery, for example, this is particularlyadvantageous in that the surgical access system 10 may be particularlysuited for establishing an operative corridor to an intervertebraltarget site in a postero-lateral, trans-psoas fashion so as to avoid thebony posterior elements of the spinal column.

FIGS. 21-22 are exemplary screen displays (to be shown on the display140) illustrating one embodiment of the nerve direction feature of themonitoring system shown and described with reference to FIGS. 19-20.These screen displays are intended to communicate a variety ofinformation to the surgeon in an easy-to-interpret fashion. Thisinformation may include, but is not necessarily limited to, a display ofthe function 180 (in this case “DIRECTION”), a graphical representationof a patient 181, the myotome levels being monitored 182, the nerve orgroup associated with a displayed myotome 183, the name of theinstrument being used 184 (in this case, a dilator 46, 48), the size ofthe instrument being used 185, the stimulation threshold current 186, agraphical representation of the instrument being used 187 (in this case,a cross-sectional view of a dilator 44, 48) to provide a reference pointfrom which to illustrate relative direction of the instrument to thenerve, the stimulation current being applied to the stimulationelectrodes 188, instructions for the user 189 (in this case, “ADVANCE”and/or “HOLD”), and (in FIG. 22) an arrow 190 indicating the directionfrom the instrument to a nerve. This information may be communicated inany number of suitable fashions, including but not limited to the use ofvisual indicia (such as alpha-numeric characters, light-emittingelements, and/or graphics) and audio communications (such as a speakerelement). Although shown with specific reference to a dilating cannula(such as at 184), it is to be readily appreciated that the presentinvention is deemed to include providing similar information on thedisplay 140 during the use of any or all of the various instrumentsforming the surgical access system 10 of the present invention,including the initial distraction assembly 40 (i.e.

the K-wire 42 and dilators 44, 48) and/or the retractor blades 12, 16,18 and/or the shim elements 22, 24, 25.

As evident from the above discussion and drawings, the present inventionaccomplishes the goal of gaining access a surgical target site in afashion less invasive than traditional “open” surgeries and, moreover,does so in a manner that provides the ability to access such a surgicaltarget site regardless of the neural structures required to be passedthrough (or near) in order to establish an operative corridor to thesurgical target site. The present invention furthermore provides theability to perform neural monitoring in the tissue or regions adjacentthe surgical target site during any procedures performed after theoperative corridor has been established. The surgical access system ofthe present invention can be used in any of a wide variety of surgicalor medical applications, above and beyond the spinal applicationsdiscussed herein. Such spinal applications may include any procedurewherein instruments, devices, implants and/or compounds are to beintroduced into or adjacent the surgical target site, including but notlimited to discectomy, fusion (including PLIF, ALIF, TLIF and any fusioneffectuated via a lateral or far-lateral approach and involving, by wayof example, the introduction of bone products (such as allograft orautograft) and/or devices having ceramic, metal and/or plasticconstruction (such as mesh) and/or compounds such as bone morphogenicprotein), total disc replacement, etc. . . .).

Moreover, the surgical access system of the present invention opens thepossibility of accessing an increased number of surgical target sites ina “less invasive” fashion by eliminating or greatly reducing the threatof contacting nerves or neural structures while establishing anoperative corridor through or near tissues containing such nerves orneural structures. In so doing, the surgical access system of thepresent invention represents a significant advancement capable ofimproving patient care (via reduced pain due to “less-invasive” accessand reduced or eliminated risk of neural contact before, during, andafter the establishment of the operative corridor) and lowering healthcare costs (via reduced hospitalization based on “less-invasive” accessand increased number of suitable surgical target sites based on neuralmonitoring). Collectively, these translate into major improvements tothe overall standard of care available to the patient population, bothdomestically and overseas.

What is claimed is:
 1. A system for accessing a surgical target site, comprising the steps of: a retractor assembly having a plurality of blades releasably coupled to a handle assembly, said plurality of blades capable of being advanced simultaneously to said surgical target site while in a closed position and thereafter selectively opened to create a customized operative corridor to said surgical target site. 